1. Field of the Invention
The present invention relates to facsimile machines, and in particular, relates to facsimile machines including data access apparatuses in the form of semiconductor devices.
2. Description of the Related Art
In order to reduce the size of facsimile machines, data access apparatuses in the form of semiconductor devices are used in interfaces (I/Fs) between the facsimiles machines and telephone lines. These data access apparatuses in the form of the semiconductor devices are expressed as semiconductor data access arrangement (DAA) or SiDAA. Moreover, the facsimile machines are configured such that external telephones can be connected thereto and such that the facsimile machines and the external telephones can use the same telephone lines. Japanese Patent Laid-Open No. 9-8950 describes a structure that detects current using an off-hook detector 2 disposed between an external telephone and a telephone line as shown in FIG. 8 so as to detect the on-hook/off-hook state of the external telephone. Moreover, Japanese Patent Laid-Open No. 2005-57659 describes a structure that detects changes in line voltage in accordance with the on-hook/off-hook state of an external telephone using a voltage-detection function included in a SiDAA as shown in FIG. 9.
However, the structure described in Japanese Patent Laid-Open No. 9-8950 uses line current obtained by the off-hook detector 2 disposed at a primary side of the line for detecting the on-hook/off-hook state of the external telephone. With this structure, the direction of the line current changes in accordance with the connection state of the line. Therefore, the detector needs to detect bidirectional current, and the configuration of the current detection circuit of the detector becomes complicated. This prevents size reduction of the circuit.
Moreover, the structure described in Japanese Patent Laid-Open No. 2005-57659 cannot detect the on-hook/off-hook state of the external telephone after SiDAA is connected to the line for facsimile transmission/reception.